The long-term goal for this research is to identify modifiable etiologic risk factors for illegal drug self-administration by children and teenagers. In the research, a preventive trial and a nested case-control study will be conducted to examine two potential risk factor relationships in detail. Specific hypothesis #1 concerns the potentially causal significance of the relationships between disobedience, aggression, and drug-related behavior. Specific hypothesis #2 concerns the potentially causal significance of the relationship between learning problems and drug-related behavior. In the field experiment to examine these hypotheses, randomization and other features of the experimental method will be used to control error. In addition, the data analysis plan is multivariate and provides for estimation of the experimental intervention effects, conditionally on other potential determinants of drug-related behavior. The sample for the field experiment consists of more than 2000 children in early elementary school classrooms of the Baltimore City Public Schools. Roughly 1/4 of the children are assigned to the Good Behavior Game intervention, which is designed to reduce the occurrence of disobedience and aggression; roughly 1/4 are assigned to a Mastery Learning intervention designed to reduce the occurrence of learning problems; the remainder receive no special intervention. If these interventions work as planned, disobedience, aggression, and learning problems will be less common. With a five-year followup, assessment of a potential impact on illegal drug self-administration should be possible. However, the research is designed to add substantially to our knowledge of potential determinants of drug self-administration, even if the interventions are weak or even inert.